A bevel gear is designed primarily to have an involute tooth form so that a rolling action takes place between meshing teeth, and line contact exists between at least one pair of meshing teeth of two inter-engaging gears at all time during rotation. However there are some difficulties encountered when relatively small gears are required, as for example in the case of the meshing gears between a toothed nut and a handle spindle pinion of a rotary clothes hoist required to inter-engage for elevation of the upper movable standard.
In the first instance, the length of the teeth is relatively great, and to avoid undercut conditions it is necessary to have more than 13 teeth for an involute form. This in turn means that the teeth are relatively small in size, and consequently are not mechanically strong if formed for example from plastics material. It is desirable that the teeth be relatively large if formed from plastics material so that the danger of fracture at the root is reduced. Bevel gears are essentially precision devices, and will not tolerate large dimensional errors of angle or dimension. Furthermore the cost of forming a die for bevel teeth is relatively high.
The main object of this invention is to provide a satisfactory angle meshing gear which can have relatively large teeth although the gear is of relatively small diameter, and wherein the construction is so simple that the die costs are relatively small.